1. Field of the Invention
The present invention relates to an image forming method and an image forming apparatus.
2. Description of the Related Art
In recent years, in an electrophotography process for forming images, demands for high image quality and high stabilization have been increased.
Herein, in the electrophotography process, as a method of realizing high image quality, there is a method of reducing a beam size for exposure. According to the method of reducing the beam size for exposure, small electrostatic latent images are formed, so that resolution can be increased.
However, controlling an image height of the formed electrostatic latent image while reducing the beam size for exposure is difficult and causes high cost in image formation.
In addition, the cost of the controlling the image height of the formed electrostatic latent image while reducing the beam size for exposure accounts for a large fraction of the entire cost of the image forming apparatus.
Therefore, in the electrophotography process, there has been a requirement for forming micro-sized electrostatic latent images without reducing the beam size for exposure.
In addition, in the image forming method of the related art, a line image and a solid image are different in toner adhesion amount height, that is, a pile height. The difference in pile height is caused from a difference in size itself of the electrostatic latent image.
As described above, by considering the demand for improvement of image quality and the demand for reduction of environmental burden such as reduction of toner usage or reduction of power usage, there has been a need for appropriately controlling the pile height.
Here, in the case of controlling the pile heights of the line image and the solid image, a method of performing treatment in a developing process is conceivable.
However, since the line image and the solid image have a difference in size itself of the electrostatic latent image, in order to control the pile height in the developing process, developing needs to be performed by differentiating sensitivity of the latent image of the line image and sensitivity of the latent image of the solid image.
That is, the method of controlling the pile height by setting the sensitivity of the latent image of the line image and the sensitivity of the latent image of the solid image to be different from each other is not preferred because there is a problem such as a loss in fidelity of the latent image.
As described above, in the image formation, controlling the pile height without performing treatment in the developing process is desired. In addition, in the image forming method, desired is a method of forming an electrostatic latent image such that the difference between image data and output image occurring in the electrophotography process, other than the pile height, can be offset.
In addition, there is disclosed a technique where, in the image formation, in the case where an area of input image is smaller than a predetermined value, exposure energy per unit pixel is set to be higher than the exposure energy per unit pixel at the time of solid image writing (for example, refer to Japanese Patent Application Laid-open No. 2005-193540).
In addition, there is disclosed a technique where, in the image formation, light energy exposed from each light source is corrected to be uniform by thinning out exposure pixels or adding the exposure pixels (for example, refer to Japanese Patent Application Laid-open No. 2007-190787).
In the image formation, in the case where a dot density is high, for example, 1200 dpi, there is a demand for an output image where micro-sized characters corresponding to two or three points, particularly, a character of a reversed image becoming two or three void points can be recognized.
However, in the image formation, although developing, transfer, and fixing processes are improved in order to output a high-quality image with a high dot density, the outputting the high-quality image has been difficult.
Here, although the measuring the electrostatic latent image in a micrometer scale was difficult, in recent years, the measurement of the electrostatic latent image at a high accuracy has been enabled. As a result, it is found out that degradation factor in the image formation is generated in the latent image stage before the developing.
That is, it is found out that, even though the reversed image is output using the image pattern as is, a latent image electric vector in a vertical direction of a sample occurring in a normal image is not reversed, and a vector of the reversed image is smaller than a vector of the image pattern.
Therefore, in the image formation, in the case of outputting a micro-sized image with a high dot density, discrepancy occurs between the latent image and an image pattern signal supplied from a controller due to influence of the beam size or charge diffusion. For this reason, in the image forming method, in the case of outputting a micro-sized image with a high dot density, even if the developing, transfer, and fixing processes are improved, a high-quality image could not be output.
Particularly, in order to print a character of the reversed image with a high image quality, it is effective to increase the latent image electric vector in the vertical direction of the sample towards such a side that toner is made not to adhere. In terms of electromagnetism, the simplest method of increase the electric vector in a white portion is to increase a charge amount in a white image portion. However, it is difficult to locally increase a electrification charge amount.
There is a need to provide an image forming method capable of forming a high-quality image by an image pattern including an image portion composed of a plurality of pixels and a non-image portion.